Electromagnetic fields linked to asthma

2nd August 2011

Pregnant mothers who are exposed to low-level magnetic fields may have a much higher risk of giving birth to asthmatic children, according to a recent US study.

The researchers found that childhood asthma was more frequent among babies that had been exposed to a lot of low-level electromagnetic fields, like those that arise when appliances are used or when electricity moves through power lines, while still in the womb.

In previous studies, scientists had asked their study subjects to estimate their own chronic exposure to electromagnetism.

For the recent study, the researchers avoided guesswork, asking their subjects to wear a monitor in an initial prospective study.

In that study, 801 women measured their own exposure to low-frequency electromagnetic fields, including fields generated by fluorescent light bulbs, power stations, and kitchen appliances.

The monitor did not pick up fields created by mobile phones and mobile phone masts, since those devices use a much higher frequency at the other end of the electromagnetic spectrum.

After the initial prospective study, the researchers followed the women's children by looking at medical records.

More than 20% of the children developed asthma, and the researchers were able to estimate that many of these children had been exposed to chronic, low-level electromagnetism in the womb.

Women in the top 10% of electromagnetic exposure were more than three times as likely to give birth to asthmatic children as women who were exposed to the lowest 10% of the exposure range.

And children whose mothers were exposed to moderate levels of electromagnetic radiation still had a very high risk of developing childhood asthma.

Being somewhere between 10% and 90% of the exposure range seemed to bring a 75% increased risk of childhood asthma, compared to children whose mothers were in the lowest exposure group.

Lead author De-Kun Li, a senior researcher at Kaiser Permanente in Oakland, California, said that children of women whose exposure levels were in the range of the bottom 10% group seemed to have about a 14% risk of developing asthma.

Researchers estimate that about 13% of all children and teenagers have asthma.

Li said that, although the reason why electromagnetism would end up affecting people in such a way was not clear, he and colleagues had conducted a previous study that found a link between exposure and misscariages.

People's immune responses also seem to be altered.

Li said he believed that the issue of electromagnetism and human health needed to be studied and not dismissed as it had been in the past.

He said that, if other studies can confirm his finding, researchers may one day have new ways of preventing asthma.